Later on, Wilson stops by House's office and reports that his "mutinous team" is "starting to worry about life on Pitcairn Island," since House's biopsies are clean thus far. They should worry about life on Pitcairn, too; after that mutinous Bounty crew landed there, all the Tahitian men they took with them got pissed off at the lack of women and rights and ended up slaughtering most of the crew. Bad times. Since the blood seems to be fine after all, Flynn has been scheduled for some bone-marrow irradiation. Then Wilson gets annoying and psychoanalyzingy and points out that House risked his life yet again by getting a transfusion of possibly tainted blood. House says that he would've made Foreman do it, but that House is the only one with Flynn's blood type. Wilson points out that AB is a very fitting type for House, since it's the one all other types can donate to. House says Wilson is Type O, making him the blood type that can donate to everyone else. I guess we know who gives and who receives in that relationship. Wilson just wants to know how House knows Wilson's blood type and what evil genius plan of his he tested Wilson's blood type for without Wilson's knowledge. This gives House an idea.
House leaves his office and intercepts Flynn's gurney as it's on its way to radiation treatment. House dismisses the nurse/orderly/whoever pushing the bed by saying that it's too late and Flynn is a dead man. They shrug and walk off in separate directions, as you would. Flynn is thrilled to bits that he'll go out having predicted his own death. House tells him that his magic secrets shouldn't go to the grave with him, but Flynn doesn't bite. He'll never tell how he did that card-on-the-other-side-of-the-glass thing. Once House is sure that there's no way he'll get the trick out of Flynn no matter how many lies he tells, he reveals that Flynn isn't dying after all. I guess this is House's week to make everyone think they're dying so he can get his jollies. He asks Flynn what his blood type is. "A," Flynn responds immediately. I have no idea what my blood type is. Off House's triumphant expression, Flynn asks him what's up. "It's way cooler to know," House says.
With that, House enters the radiation room and tells the waiting Numbers and Foreman that he solved the mystery: Flynn doesn't have amyloidosis. Good thing they weren't about to destroy his immune system unnecessarily, then. What Flynn does have is a circulatory system full of the wrong blood type, which caused all of his post-surgery symptoms. When they tested Flynn's blood type for the transfusion, they tested for antibodies. Even though Flynn is Type A, he had Type B antibodies in his blood, making it appear as though he was Type AB. And just what caused the B antibodies as well as Flynn's pre-surgery symptoms? An autoimmune disease, which caused his antibodies to, as Thirteen says, "go haywire." And which autoimmune disease does Flynn have? "I finally had a case of lupus!" House cheers. If only he hadn't chopped up his lupus textbook, he could've diagnosed this so much earlier. And if only the blood bank did proper blood type testing procedures, Flynn never would've been given the wrong blood type in the first place. Maybe they were too busy playing Solitaire to do their jobs that day, though. Oh well. House tells the Numbers to give Flynn the correct blood and some steroids and he'll be just fine, because lupus isn't a painful and potentially fatal disease with no cure or anything like that.